code: def value(self, k=-1):
      if k != -1:
          if k not in self.sum.keys():
              raise AssertionError(
                  "invalid k (this k was not provided at construction time)"
              )
          if self.accuracy:
              return (1.0 - float(self.sum[k]) / self.n) * 100.0
          else:
              return float(self.sum[k]) / self.n * 100.0
      else:
          return [self.value(k_) for k_ in self.topk]
  
file_path: pywick/pywick/meters/classerrormeter.py
imports: import numpy
  import torch
  import numbers
  from .None import meter
label_desc: Use image node_id 4 for calling the ClassErrorMeter obj's underlying member method code with example usage: obj.value(k) and returns: unknown, unknown, unknown